As a power semiconductor device with which a low on resistance and a high breakdown voltage are required, it has used a vertical semiconductor device by which electrodes are disposed on the both principal surfaces of a semiconductor substrate, respectively. For example, in a vertical power MOS field-effect transistor (MOSFET), current flows through a drift region inserted into between a source region and a drain region formed on the both principal surfaces of the semiconductor substrate, respectively. The drift region is a current path when the power MOSFET is turned ON, and the drift region is depleted and then the value of a breakdown voltage is improved when the power MOSFET is turned OFF.
In order to reduce the on resistance of the power MOSFET, it is effective to reduce an electric resistance of the drift region by improving a high impurity concentration of the drift region. However, if the high impurity concentration of the drift region is improved, the extension of a depletion layer becomes unsatisfactory, and then the value of the breakdown voltage is reduced. That is, there is a trade-off relationship between the high breakdown voltage and the low on resistance.
For this reason, it is proposed about a power MOSFET having a drift region of super-junction structure (for example, refer to Patent Literature 1). The drift region of the super-junction structure has a structure which disposes a pillar of p type semiconductor region and a pillar of n type semiconductor region alternately along the principal surface of the semiconductor substrate. The drift region is depleted by the depletion layer extended from a pn junction interface formed of the p type semiconductor regions and the n type semiconductor regions, and then the value of the breakdown voltage of power MOSFET is held. Therefore, even if the extension of the depletion layer becomes small by improving the high impurity concentration in order to achieve the low on resistance, the drift region can be completely depleted by narrowing the width between the pillar of the p type semiconductor region and the pillar of the n type semiconductor region. Accordingly, the low on resistance and high breakdown voltage of the power MOSFET are achievable.